QTL mapping of stay-green-related traits in wheat under drought condition

Drought is the primary abiotic stress that significantly affects wheat production. Extending the duration of leaf greenness, thereby increasing photosynthetic time and efficiency, is crucial for wheat in ensuring organic matter accumulation under drought stress and ultimately stabilizing wheat yield. Understanding the developmental and genetic characteristics of flag leaf greenness retention in wheat and identifying stable molecular markers closely associated with greenness-related genes, independent of environmental influences, can significantly accelerate the breeding process for drought resistance. In this study, we utilized a DH population consisting of 174 lines derived from Yangmai 16 and Zhongmai 895 as experimental materials. We conducted phenotypic evaluations of the percentage of green leaf area (GLA) and relative chlorophyll content (SPAD value) in flag leaves at 10 d, 14 d, 18 d, 22 d, 26 d, and 30 d post-flowering under two moisture environments: normal drip irrigation (NI) and drought stress (DS). We simulated the change in GLA using the Gompertz model and performed QTL mapping for eleven greenness-related traits, including time to maximum senescence rate (TMRS), green leaf area duration (GLAD), average senescence rate (ARS), time to the beginning of rapid senescence (T1), time to the end of rapid senescence (T2), and the dynamic SPAD value of the flag leaf. The results revealed a phenomenon of transgressive segregation in GLA, aging characteristic parameters, and dynamic SPAD values of the DH population and parents under both well-watered and drought conditions, demonstrating certain differences. A consistent trend of slow-rapid-slow decline in GLA was observed at different time points across all families and parents, with rapid senescence primarily occurring at 18 d, 22 d, and 26 d Except for the negative correlation between ARS and GLA-10D, positive correlations were observed among all other traits. The heritability of each trait ranged from 0.50 to 0.81. Linkage analysis identified a total of 27 stable loci associated with greenness retention in wheat across two or more environments. Among these, 11 loci were associated with wheat senescence characterization trait parameters, and 16 loci were associated with dynamic SPAD values of the flag leaf. These loci were distributed on chromosomes 1A, 1B, 4B, 4D, 5D, 7B, and 7D, explaining 3.86%-14.11% and 2.99%-17.45% of the phenotypic variance, respectively. One QTL regulating T1 and five SPAD values on chromosomes 4B, 4D, and 7B were consistently detected across the three environments, explaining 8.97%-14.11% and 6.85%-17.45% of the phenotypic variance, respectively. The results of QTL co-localization effect analysis revealed that loci containing Rht-D1b and AA genotypes exhibited significant enhancement and cumulative effects on SPAD-10D, while loci containing GG and TT genotypes showed significant enhancement and cumulative effects on SPAD-18D. Four QTL clusters with significant effects were identified on chromosomes 4B, 4D, 7B, and 7D. Notably, the segment of the QTL cluster on chromosome 4D (18.80-28.58 Mb) remained unaffected by water availability and contained the Rht-D1 gene. The loci regulating SPAD-0D and SPAD-10D might be influenced by the multiplicative effect of this gene. Candidate gene analysis identified eight candidate genes, such as TraesCS4D01G054000, TraesCS1B01G434300, and TraesCS7B01G010200, which are associated with greenness retention. These findings provide a theoretical foundation for molecular marker-assisted breeding aimed at improving greenness retention in wheat.